The inadequate treatment of municipal solid waste that is being put in landfills and the increasing addition of nondegradable materials, including plastics, to municipal solid waste streams are combining to drastically reduce the number of landfills available and to increase the costs of municipal solid waste disposal. While recycling of reusable components of the waste stream is desirable in many instances, the costs is of recycling and the infrastructure required to recycle materials is sometimes prohibitive. In addition, there are some products that do not easily fit into the framework of recycling. The composting of non-recyclable solid waste is a recognized and growing method to reduce solid waste volume for landfilling and/or making a useful product from the waste to improve the fertility of fields and gardens. One of the limitations to marketing such compost is the visible contamination by undegraded plastic, such as film or fiber fragments.
It is desired to provide components that are useful in disposable products and that are degraded into less contaminating forms under the conditions typically existing in waste composting processes. Such conditions generally include temperatures of about 70° C. or less, and averaging in the 55-60° C. range; humid conditions as high as 100 percent relative humidity; and exposure times that range from weeks to months. It is further desirable to provide disposable components that will not only degrade aerobically/anaerobically in composting, but will continue to degrade in the soil or a landfill. As long as water is present, the components preferably continue to break down into lower molecular weight fragments, which can be ultimately biodegraded by microorganisms completely into biogas, biomass, and liquid leachate, as occurs with natural organics like wood.
The present invention provides aliphatic-aromatic copolyetheresters. In preferred embodiments, the aliphatic-aromatic copolyetheresters are biodegradable. The aliphatic-aromatic copolyetheresters can be formed into articles such as films, sheets, and containers.
Aliphatic-aromatic polyetheresters generally include polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids, which also incorporate poly(alkylene ether) glycols. Generally, known aliphatic-aromatic copolyetheresters incorporate high levels of the poly(alkylene ether) glycol component. For example, Witsiepe, in U.S. Pat. No. 3,651,014, Barbee, et al., in U.S. Pat. No. 4,328,333, and Tung, in U.S. Pat. No. 4,390,687, disclose aliphatic-aromatic polyetherester compositions that include high levels of poly(alkylene ether) glycol. The high levels of the poly(alkylene ether) glycol typically translate to lowered thermal properties of the aliphatic-aromatic copolyetheresters. For example, Warzelhan, et al., disclose aliphatic-aromatic polyetherester compositions in U.S. Pat. Nos. 5,936,045, 6,046,248, 6,258,924, and 6,297,347 that have 20-25 mole percent of the poly(alkylene ether) glycol component and are found to have lowered crystalline melting point temperatures in the range of 111° C. to 127.5° C.
Aliphatic-aromatic copolyetheresters have also been disclosed that include mixtures of glycol components. The use of such mixtures has also been disclosed to lead to reduced thermal properties of the aliphatic-aromatic copolyetheresters. For example, Kinkelin, et al., in U.S. Pat. No. 6,255,443, disclose aliphatic-aromatic polyetherester compositions that contain glycol mixtures of nearly equal levels of 1,4-butanediol and 1,6-hexanediol. The resulting aliphatic-aromatic copolyetheresters were disclosed to have lowered crystalline melting point temperatures in the range of 78° C. to 89° C.
Known aliphatic-aromatic copolyetherester compositions and films derived therefrom have not been shown to provide high temperature characteristics, which are desired for many end uses, such as films, coatings and laminates, combined with excellent biodegradation rates. Although the use of blends to form biodegradable materials is known, as disclosed in WO 02/16468 A1, to provide certain film physical properties, the use of polymeric blends necessarily complicates the processes used to produce films, coatings, and laminates. The aliphatic-aromatic copolyetheresters disclosed herein do not require blending and provide biodegradable compositions having advantageous physical properties. The present invention provides aliphatic-aromatic copolyetheresters with improved combinations of thermal properties and biodegradation rates as compared to known aliphatic-aromatic copolyetheresters.